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Chemistry · Organic · Bromine water test
Testing for unsaturation
Bromine water is orange. When shaken with a substance that contains a C=C double bond (an alkene, an unsaturated oil), Br₂ adds across the double bond and the colour disappears. Saturated compounds do not react.
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Observations
Hexane (C₆H₁₄)
Hex-1-ene (C₆H₁₂)
Cyclohexane
Cyclohexene
Sunflower oil
Animal fat (lard)
Exam-style questions
1. Why does bromine water turn from ORANGE to COLOURLESS in the presence of an alkene?
2. Which homologous family contains C=C double bonds and therefore DECOLOURISES bromine water?
3. Sunflower oil decolourises bromine water; lard does not. What does this tell you?
4. Write the ADDITION reaction for ethene with bromine.